I don’t have a clue, but could figure it out how to setup a dhcp forwarder on the Aruba/Procurve switch. But I would have to say, if you have a single dhcp server today AND you have vlans in place then you should have a dhcp-helper/dhcp-relay service already installed on your vlan/subnet router. The only reason why you would need to change this service is if you are running dnsmasq service on your fog server (something you would intentionally turn on and configure). If you are not using dnsmasq then changing the dhcp-relay service is not needed.

Can you explain a bit more about what issue you are having?